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A/C whining after shutoff -- pressure equalizing?

In December I had a new heat pump installed, and since I've begun running the a/c, I've had a strange issue. After the a/c shuts off, it starts to emit a high pitched whining/buzzing noise of varying loudness and tone for a few minutes afterwards. It's loud enough that I can hear it in a quiet room of my house, but not very loud. It seems to be coming from the air handler in the area where the line set goes into it. Completely shutting off the electricity to the system makes the sound go away.

Some web searching seems to indicate this may be a normal sound of pressure equalization in the line set, but I never heard it in my old heat pump, and it seems strange that cutting the power makes it stop. Does anyone have any clue what this might be? Is this sort of sound normal? I don't want to go calling my HVAC company if they're gonna tell me there's nothing to be done about it.

What's the brand, model and serial of the condenser? A specific brand has had issues with a tea pot whistle sound.

The outdoor unit is a Trane 4TWX5024B1000AA. But the sound is coming from the indoor unit (TAM7A0A24H21SBB).

I guess I'm trying to figure out how common an issue this is, if at all, and what the odds are of it actually being made better. If this is a common problem where a simple part swap will fix it, then I'd do it; but if the noise is normal and there's not a good chance of eliminating it completely, I'd just as soon not skip work to have it looked at.

A/C whining after shutoff -- pressure equalizing?

I had a feeling you were going to say Trane.

The noise is coming from the indoor EEV. During a shutoff period, the EEV closes to step position 56, which is almost closed but not all the way. Since it doesn't close all the way, this will create a teapot whistling sound in certain applications.

The sound is from the refrigerant squeezing through the EEV.

Trane has remedied this issue by reconfiguring the EEV control board. All new boards close the EEV all the way during a shut off.

Call you installing contractor, tell him your issue, he can order a new board and install it. Part should be under warranty. Easy fix.

Thanks for the help. Out of curiosity, is there some sort of reference from Trane regarding this, like a service bulletin?

No bulletin out (yet). Trane has to have A LOT of the same issue before a service bulletin is issued. We covered the tea pot whistle in the fall update and was told the new board part number. I always keep the handouts from the update classes so I will search for it and post it (if I can find it).